A 5' spliced leader is added in trans to both alpha- and beta-tubulin transcripts in Trypanosoma brucei.

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Abstract
The approximately 15 .alpha.- and 15 .beta.-tubulin genes of Trypanosoma brucei are arranged in a tandem array of alternating .alpha.- and .beta.-tubulin genes. We have examined the structure of mRNA transcripts from the tubulin gene family and have found at the 5'' ends of both .alpha.- and .alpha.-tubulin messages a 35-nucleotide spliced leader (SL) identical to that identified previously on the 5'' ends of variant surface glycoprotein (VSG) mRNAs. No 35-nucleotide SL sequences were encoded in the tubulin intergenic regions; instead, the SL sequence apparently originates from small RNA transcripts encoded at sites that are unlinked to the tubulin genes. The tandem arrangement of the tubulin genes and the presence of the SL at the 5'' end of both .alpha.- and .beta.-tubulin transcripts establishes that RNA joining between the SL and tubulin mRNA occurs in trans.